German Patent Disclosure Document No. DE-OS 22 28 625, inventor Simeth, discloses a doctor blade for use in an inker of a printing machine in which the doctor blade is subdivided by slits, which slits are filled with a plastic material. Filling the slits with plastic material permits adjustment of the tongues formed by the subdividing slits, individually, with respect to the doctor blade so that the individual tongues are decoupled from each other to permit adjustment of one tongue, for example, without interfering with the position of an adjacent tongue. It has been found that in operation adjustment of two adjacent tongues in opposite direction may cause separation of the plastic layer between the respective tongues from the metallic material of which the doctor blade is usually made. It is customary to make doctor blades of spring steel or similar material. It appears that the cause for separation of plastic material from the doctor blade itself is based on insufficient adhesion of the plastic material on the metallic doctor blade with respect to shearing forces; in other words, the resistance to shearing occurring between the elastic filling material and the hard material of the doctor blade, in addition to the hydrostatic pressure occurring in operation of the printing machine, causes forces tending to separate the plastic material from the knives. The forces are substantial and act on the elastic filler material.
The elasticity of the filler material of the doctor material disclosed in the German Patent Disclosure Document No. DE-OS 22 28 625 causes the gap of the doctor blade, that is, the distance between the longitudinal edge of the doctor blade adjacent the inker roller and the inker roller itself to be different in the region of a slit, so that rings of ink will arise on the inker roller, which is undesirable. This effect may even increase if the filler material in the slits, in the metering range of the doctor blade, wears faster than the doctor blade itself.
It has previously been proposed to cover the slits between the tongues which will be the result of the slits, and which project towards the ink roller. U.S. Pat. No. 2,837,024 describes an arrangement in which the slits are covered. German Pat. No. 24 60 116 describes a cover in form of a foil, applied at the inside of the ink trough. This arrangement causes substantial wear on the foil, thus requiring frequent exchange of the foil elements. If a cover is applied, for example by adhesion, at the bottom of the doctor blade, the penetration of ink between the doctor blade and the cover is unavoidable. The cover may be adhered and, upon adjustment of the tongues for control of ink flow in the respective zones, ink may penetrate through the slits in the region of adhesion between the cover and the doctor blade, resulting, eventually, in undesirable removal of the foil from the doctor blade and, additionally, to drying of ink in the region of penetration which, eventually, will lead to inoperability of the doctor blade.